Driver Education 101: What motorists should know about when and how to sound a car horn:Tennessee law requires all motorized vehicles on the road to be equipped with a horn. In fact, the Tennessee Driver’s Handbook says: “The horn may not seem like it is important for safety, but as a warning device, it could save your life.”The handbook also says a driver should “only use your horn as a warning to others.”That’s right — a horn should be used as a warning (applied in short bursts), not as a blaring editorial comment on another motorist’s driving skills. Too often, however, you hear the bast of a car horn, followed by an angry shout of profanity that is accompanied by a vulgar hand gesture coming from an impatient driver.The National Highway Transportation Safety Administration said these actions are all signs of aggressive driving. The Tennessee Driver’s Handbook also notes you might be an aggressive driver if you:Speed up when someone tries to pass you, tailgate people who are going slower than you, weave in and out of traffic lanes or pass cars on the right shoulder. Flash your headlights at vehicles to get them to let you pass, use your car horn when angry or upset with traffic jams or other drivers.DriversEdGuru.com notes that honking a horn will not “magically” clear up a traffic jam. The website also says that blasting a horn to vent frustration will just tick other drivers off.“Unless you are in a parade or stuck in a parking garage after your favorite baseball team just won the World Series, you should never lay on your horn in traffic,” the website notes.Gratuitous horn-honking may also be against the law in some areas of the state. Many cities and towns have ordinances that prohibit blowing a car horn in neighborhoods and near certain businesses at specific times of the day. As we said earlier, Tennessee law requires “every motor vehicle, when operated upon any road, street or highway of the state, shall be equipped with a horn in good working order capable of emitting sound audible under normal conditions from a distance of not less than 200 feet.”It is against the law, however, for a vehicle “to be equipped with or for any person to use upon a vehicle any siren, exhaust, compression or spark plug whistle or for any person at any time to use a horn otherwise than as a reasonable warning or to make any unnecessary or unreasonably loud or harsh sound by means of a horn or other warning device.”That means a diesel train whistle is not acceptable for street use.